Decontamination of food products such as seeds, grains, nuts, spices, dried and dehydrated foods and fruits to rid them of yeast, molds, fungi, bacteria (and other microorganism), insect larvae and eggs, insects and mycotoxins produced by certain fungi, including species of Penicillium and Aspergillus, is an important concern for food growers, packagers, processors and consumers. How best to treat such foods products without damaging the appearance, texture, taste or other organoleptic properties of the food and without imposing environmental or health risks, e.g. depositing carcinogenic or mutagenic chemicals onto the foods or releasing such chemicals into the environment, because of such treatments has long been an area of investigation. Currently, propylene oxide is commonly used to decontaminate food products. Unfortunately, propylene oxide treatment poses undesirable environment and carcinogenic risks. Other decontamination treatments involve the use of ethanol, methyl bromide, chloropicrin, and hypochlorite.
For purposes of this invention, the word decontamination is used to indicate that the food products have been rid of the undesirable organisms to enhance the shelf life and processing attributes of the food, including meeting the Federal Food and Drug Administration guidelines and food processor specifications. The word is meant to include the concepts of disinfestation and fumigation as well.
Current decontamination techniques do not decontaminate foods of all bacteria, molds, yeast or decompose mycotoxins found on food products. For example, Tilletia controversa, the causal agent of dwarf bunt of wheat, a disease occurring primarily in winter wheat growing in regions having prolonged snow cover is particularly difficult to kill. In fact, because there is no known occurrence of Tilletia controversa in the Peoples Republic of China (PRC), the PRC requires that imported wheat be free of T. controversa teliospores. Accordingly, wheat from the United States is often not imported into the PRC. An economically feasible method to decontaminate wheat containing T. controversa is a solution to this problem.
The present invention overcomes the above described disadvantages of current decontaminate methods by decontaminating food products by exposing the food products to vapor phase hydrogen peroxide wherein the hydrogen peroxide vapor is generated from a multi-component solution and wherein the ratio of the hydrogen peroxide in the vapor is substantially the same weight percent composition as the liquid solution from which it was generated. In a first embodiment, the food product is exposed to one treatment of an effective amount of hydrogen peroxide vapor. This method has application at above, below and at ambient pressures. The liquid hydrogen peroxide concentration can be in any amount, preferably, but not limited to, from about 25-70%, while the concentration of vaporized hydrogen peroxide preferably ranges from 0.5-10 mg hydrogen peroxide/Liter volume of the exposure chamber or flow-through apparatus. The exposure chamber can be maintained at ambient, above and below ambient temperature. Achieving a hydrogen peroxide vapor concentration that is substantially the same weight percent composition as the liquid solution can be accomplished by any procedure which will flash vaporize the hydrogen peroxide solution. The appropriate concentration of hydrogen peroxide, exposure time, exposure pressure or vacuum, or flow-rates must be determined for each food product. These conditions must be determined empirically and will depend upon several factors, including:
1. surface area to volume ratio of the food product; PA1 2. type of surface (i.e. skin, shell, casing) PA1 3. presences of oil or fats; PA1 4. level of cellulosic material present; PA1 5. whether a batch, continuous or semi-continuous process is used; and PA1 6. temperature at which one wishes to treat the product.
U.S. Pat. No. 4,642,165, provides an explanation of a method that achieves flash vaporization and that disclosure is incorporated herewith by reference. A product currently providing the appropriate flash vaporization is AMSCO's VHP Sterilizer. The equation for calculating hydrogen peroxide vapor concentration in an AMSCO VHP Sterilizer is as follows. ##EQU1## The injection rate and hydrogen peroxide concentration are for liquid hydrogen peroxide. The term "SCFM" means standard cubic feet/minute.
In another embodiment of this invention, vapor-phase hydrogen peroxide is generated by an AMSCO VHP Sterilizer. This instrument was used to produce hydrogen peroxide vapor from 35% hydrogen peroxide solution that is drawn into the sterilizer which is an air tight chamber by vacuum. The sterilization cycle consists of three phases: dehumidification of the chamber atmosphere, generation of hydrogen peroxide vapor, and aeration. The hydrogen peroxide vapor, at a concentration of 3-4 mg/L within the chamber during fumigation, does not condense from the vapor state, and no free water is present to influence its action. It may be desirable to preheat the food product and/or the chamber to a sufficient temperature in order to avoid any condensation. Running at higher temperatures can also permit higher injections of hydrogen peroxide, thus potentially enhancing the kill rate. One or more treatment cycles are possible. For example, when two operating cycles are employed, one may be a deep vacuum (ca. 38 mm Hg, cycle 1) and the other a shallow vacuum (ca. 400-580 mm Hg, cycle 2) to inject the hydrogen peroxide vapor. Both cycles are aerated by deep vacuum evacuation of the chamber to remove residual hydrogen peroxide vapor followed by introduction of fresh air. The exhaust vapor is passed through a catalytic cell that oxidized the hydrogen peroxide to water and oxygen. The chamber temperature is normally 45-50 degrees C during a sterilizing cycle, although the temperature may be increased or decreased as determined necessary for effective treatment. In this process, the food product is exposed to the hydrogen peroxide for from about 3 to 30 minutes in each of the exposure steps to achieve a reduction in microbial levels. Exposure time may be increased or decreased to achieve the most efficient and effective treatment.
In an another embodiment of the present invention, rather than using an instrument where the food product is placed inside a chamber and removed in batch size quantities, it is contemplated that a conduit means will be used to pass the pre-sorted food product through a chamber being supplied by the hydrogen peroxide vapor generator. Such a conduit means can include, for example, a conveyor belt, an auger system or a shute system. The food product may then be aerated to remove the peroxide residuals by a variety of methods, for example, heating, subjecting the product to a vacuum, and supplying a volume of air or other gas over the product. The food is then conveyed to be finally packaged or proceed to further processing.
Although presently existing instruments have exposure chambers of from less than one cubic foot to 2000 cubic feet, it is contemplated that a chamber of any size can be built to accommodate any volume of food typically and normally encountered in the food industry. When using a conveyor system an air-tight chamber need not be used when exposing the food product to the vapor. It is contemplated that such a continuous process or semi-continuous process system may have multi unit processes, which could perform additional treatments to the food.
It is further envisioned that when working with dehydrated foods that are powders a fluidized bed reactor would be needed in order to ensure uniform opportunity for the gas to contact the surface of the individual food product particles.